Scottish Marine and Freshwater Science Volume 4 Number 3: Epidemiology and Control of an Outbreak of Viral Haemorrhagic Septicaemia in Wrasse Around Shetland Commencing 2012

Executive Summary

An outbreak of Viral Haemorrhagic Septicaemia ( VHS), as defined by European Community Council Directive 2006/88/ EC, was detected during December 2012 in multiple species of wrasse (Labridae) stocked onto six sea-water sites around Shetland Mainland. The wrasse were originally captured from the wild off the west coast of the Scottish mainland and were being used as a biological control of sea-lice (Caligidae) on Atlantic salmon ( Salmo salar) farms.

Inspection, diagnostic testing, contact tracing, epidemiological enquires and other relevant research were undertaken as part of an outbreak investigation, containment areas were established, and the removal of stocked wrasse was initiated. To date three of the six affected sites have been cleared with a substantial proportion (≈99%) of wrasse removed from the remaining sites.

Species other than wrasse were also tested for VHS. Lumpsucker ( Cyclopterus lumpus) and Atlantic salmon stocked on VHS positive sites tested VHS negative. Wild poor cod ( Trisopterus minutus) from within the pens of a VHS positive site tested VHS positive. Free-ranging wild Norway pout ( Trisopterus esmarkii), sprat ( Sprattus sprattus), grey gurnard ( Eutrigla gurnardus), herring ( Clupea harengus), whiting ( Merlangius merlangus) and plaice ( Pleuronectes platessa) from a locality around Shetland tested VHS positive.

A qualitative risk analysis suggests that the chance of this outbreak originating from the marine environment around Shetland is moderate and alternative possibilities are either low or negligible.